1. Field of the Invention
The invention relates to a sheet treating apparatus and an image forming apparatus which can prevent any reduction in throughput and which are low in cost, and particularly to delivering means for delivering a sheet after delivered to a treating tray and treated to sheet stacking means.
2. Description of Related Art
Some of conventional image forming apparatus are provided a sheet treating apparatus for treating a sheet having an image formed thereon. This sheet treating apparatus is provided with a sheet delivering apparatus for once delivering the sheet having an image formed thereon to a treating tray and effecting treatments such as alignment and stapling, and thereafter delivering the sheet (bundle) to a stacking tray.
Now, in such a sheet treating apparatus, as sheet delivering means for delivering a sheet bundle aligned and treated by the treating tray to the stacking tray, there are known sheet delivery rollers and a sheet delivery belt provided with a sheet delivery claw (for example, Japanese Patent Application Laid-Open No. 2003-73014).
FIG. 11 of the accompanying drawings illustrates the delivery by such a conventional sheet delivery belt provided with a sheet delivery claw, and in FIG. 11, the reference numeral 504 designates an intermediate stacking portion constituting the treating tray, the reference numeral 500 denotes a sheet delivery belt, and the reference numeral 501 designates a sheet delivery claw provided on the sheet delivery belt 500. Also, the reference numeral 502 denotes a sheet delivered by the sheet delivery claw 501 with the rotation of the sheet delivery belt 500 and this sheet 502 is pushed out by the sheet delivery claw 501, and thereafter falls onto and is stacked on a stacking tray 503.
The sheet delivery claw 501 is normally in a position indicated by A in FIG. 11 in which it is retracted below the intermediate stacking portion 500, and is moved from the position indicated by A to positions B, C, D, E, F, G, H and I when the sheet 502 is to be delivered, thereby delivering the sheet 502. After it has thus delivered the sheet 502, the sheet delivery claw is adapted to be again returned to the position A.
However, in the conventional sheet treating apparatus adapted to deliver the sheet 502 by such a sheet delivery claw 501, the sheet delivery claw 501 protrudes to above the stacking tray 503, for example, in the positions indicated by G and H, until it is moved to below the intermediate stacking portion 500 after it has delivered the sheet 502 in a position indicated by F. That is, the sheet delivery claw 501 is adapted to be retracted to below the intermediate stacking portion 500 while being moved above the stacking tray 503 after it has delivered the sheet 502.
When the sheet delivery claw 501 is thus retracted while being moved above the stacking tray 503, the maximum stack height of sheets which can be stacked on the stacking tray 503 has been limited to such a height that the retracted sheet delivery claw 501 does not contact with the sheets on the stacking tray, that is, to below the passage area of the sheet delivery claw 501.
That is, in a method of causing the sheet delivery claw 501 to make one round by such a sheet delivery belt 500 to thereby deliver the sheet, a space for the sheet delivery claw 501 to be moved therein must be secured above the stacking tray and correspondingly, the stack upper limit height has been low. Also, there has been the problem that the cost of the parts of the sheet delivery belt itself is high and the cost of the apparatus becomes high.
To solve such a problem, for example, the sheet delivery claw 501 can be designed to be reciprocally moved, instead of being caused to make one round. However, in a case where the sheet delivery claw 501 is thus designed to be reciprocally moved, the sheet delivery claw 501 contacts with a sheet next delivered to the intermediate stacking portion 500 when the sheet delivery claw 501 is returned to its original position after it has delivered a sheet.
Thereafter, when the sheet delivery claw 501 is to be returned to its original position, the sheet must be stopped, and in a case where design is made such that the sheet is thus stopped each time the sheet delivery claw 501 is returned to its original position, there arises another problem that throughput is reduced.
Also, in a conventional sheet treating apparatus wherein the stacking tray is provided for upward and downward movement, the stacking tray is once moved down in order to secure a space for the movement of the sheet delivery claw 501, and is again moved up to a proper sheet stacking position after the sheet delivery claw 501 has been returned to its original position. Therefore, the sheet stacking capacity need not be decreased, but yet the next sheet must be stopped until the stacking tray is returned to the proper sheet stacking position, and this has led to the problem that throughput is reduced and structure becomes complicated and costly.
On the other hand, in a method of delivering a sheet by a sheet delivery rollers, it is unnecessary to secure a space for the sheet delivery roller 501 to be move therein above the stacking tray and therefore, the stack upper limit height can be made great, but when sheets are to be stacked on the intermediate stacking portion 504 or when the sheets stacked on the intermediate stacking portion 504 are to be aligned, it is necessary to release the nip and therefore, discretely from the rotative driving of the roller, a drive source and a mechanism for releasing the nip are necessary, and this has led to the problem of a higher cost.